This section provides background information related to the present disclosure which is not necessarily prior art.
FIG. 1 shows an exemplary embodiment of a conventional Group III-nitride semiconductor light emitting device. The Group III-nitride semiconductor light emitting device includes a substrate 10 (e.g. a sapphire substrate), a buffer layer 20 grown on the substrate 10, an n-type Group III-nitride semiconductor layer 30 grown on the buffer layer 20, an active layer 40 grown on the n-type Group III-nitride semiconductor layer 30, a p-type Group III-nitride semiconductor layer 50 grown on the active layer 40, a current spreading conductive film 60 formed on the p-type Group III-nitride semiconductor layer 50, a p-side bonding pad 70 formed on the current spreading conductive film 60, an n-side bonding pad 80 formed on an exposed region of the n-type Group III-nitride semiconductor layer 30 created by mesa etching the p-type Group III-nitride semiconductor layer 50 and the active layer 40, and a protective film 90.
The current spreading conductive film 60 is provided to facilitate a smooth current supply to the entire p-type Group III-nitride semiconductor layer 50. The current spreading conductive film 60 is formed nearly over the entire surface of the p-type Group III-nitride semiconductor layer 50, and it may take the form of a light transmitting conductive film made of ITO, ZnO or Ni/Au, or a reflecting conductive film made of Ag, for example.
The p-side bonding pad 70 and the n-side bonding pad 80 are electrodes used for supplying current and wire bonding externally.
The protective film 90 is made of materials such as silicon dioxide, and may be omitted.
As there is an increasing demand for a large area, high-power semiconductor light emitting device, finger electrodes and multiple bonding pads have been introduced to facilitate current spreading within the semiconductor lighting emitting device. For example, FIG. 2 shows one example of the electrode structure disclosed in U.S. Pat. No. 6,307,218 which describes a technology for improving current spreading by means of finger electrodes 910 equidistantly spaced apart between the p-side bonding pad 710 and the n-side bonding pad 810, following the trend towards large semiconductor light emitting devices.
However, these bonding pads and finger electrodes which are made of metallic materials are thick and have a high absorption loss of light, leading to degradation of the light extraction efficiency of the semiconductor light emitting device.
In particular, a considerable amount of the light emitted from those mesa-etched faces of the p-type Group III-nitride semiconductor layer 50, the active layer 40 and the n-type Group III-nitride semiconductor layer 30 is absorbed by the lateral sides of the electrodes, or gets lost as the light travels sideways, failing to obtain effective light emission.